Drying-control apparatus



Oct. 28 v1924.

A. E. KRICK DRYING CONTROL APPARATUS Filed April 1o 1922 2 Sheets-Sheet l l ,aa as 4 342 10 INVENTOR ATTQRN Y Oct. 28, 1924` A A. E. KRICK DRYING CONTROL APPARATUS Filed April 1Q l 1922 2 Sheets-Sheet 2 HUMnDITv.

.TAMS

TBMIE HuMlDITY TIME INVENTOR ATTORNEY Patented ct. 28, i924..

'atraen ARTHUR E. xerox, or INDIANAPOLIS, INDIANA, AssIGNoB. To 'run mrnrrr ccn- .TRoL eoMrANY, oriurnIANAroi-.IsINDIANA, AyconronA'rIoN or mDIANA.

purine-connor. APPARATUS.'

Application ledApril -10, 1922. Sen/a1 No'. 551,053.

half of the entire 'drying time or longer, in order to kee the lumber from cracking, splitting, hol ow-horning, and ,case-hardening. Evenby doing this, the bestresults were not always obtained, and the defects inentioned above to lie guarded against nevertheless frequentlyappeared; and in addition the maintenance of these high relative humidities and low temperatures so far into the drying period made a long drying period necessary.

According toqmypresent invention I both lessen' 'the time required `for drying, and obtain equally as good results if not.'

better results in the quality .of the ldried lumber.

I do this, fundamentally, by departingenvtirely from the time-honored practice of 'attempting to maintain the relative humidity j period; and instead I periodically and alternately lower such relative humidity to a very low point and then raise it to a highl point, to soften thesurface of the lumber 4 each time the cycle reaches the high point,

ly close to saturation during at least the early stages of the drying, and control this lowering and raising of the relative humidity by thev rise andfall thereof to predetermined values..

midity rapidly, and let it fall slow/ly,.stop

ping the rise when the desired maxlmunr relative-humidity point is reached, and continuing the fall until moisture is being given ofi by the lumber so slowly that the relative humidity in the kiln falls to the predetermined minimum. I prefer to raise the relative humidity by discharging live steamv in .fte the kiln; and this not only raises Athe lpart of the operation, usually for at least.

- ature, without injuring the constant or substantially so for a given I raise the relative hu` relative humidity but also temporarily raises tosome extent the temperature even within .the interior of theE lumber, largely `byreason of the latent heat which the steam gives up, and also 4temporarily adds'moisture tothe lumberat and near the surface-to permitV the. readier passage therethroughof moisture from the interior. Thus the average relative humidity is -very much lower than has heretofore been the practice, with a resultant-decrease in the time required for drying; but the periodic increases of the relative humidityl maintain the surface portions of the lumber in suitable condition for rapid drying, and yproduce a recurrent condition4 of greater temperature within the body of thelumber than outside-of the lumber in the kiln and thereby promote the driving out of themoisturc -from the interior, and facilitate this by lrecurrently adding superficial moisture to the lumber, andeffectively avoid splitting, cracking, hollow-homing and case-hardening. Moreover,-I ind itis possible to increase very materially the drying temperuality of the dried lumber obtained, whi'(i1 makes further for acceleration of the drying process.

This present application isdirected to the apparatus for obtaining this drying conl trol. The process of drying control 4which also disclosed in this application is claimed in my co-pending application Serial No. 671,111 filed October 27, 1923, for process of drying control, which co-'pendingl appli-` cation is in. part ajcontinuation of this 'present application ;for while in practicing such process'I prefer to use the apparatus claimed in the present application, such process may -be practiced otherwise. the high point preferably being at or fair- -l The accompanying drawings illustrate my invention. through a kiln equipped with a. control arsolv Fig. l is a transverse sectionrangement which I may use in carrying out my invention., with the heating and humidifying means showndiagrammatically; Fig. 2 is a section through a humidiying-steam control valve and itsv operating means, embodying my invention in one form, with the valve controlled in response 'te both dry-bulb and wet-.bulb temperatures; Fig.

-3 is a view similar to Fig. 2, but with the control-valve controlled in response to the wet-bulb temperature alone; Fig. 4 is a view somewhat similartol'ltig 2, but with automeans 12, and with any suitable arrange` ments for supporting the lumber or other material to be'dried, such as the tracks 13 l'or supporting trucks which carry such lumber. is shown, both the heating means 11 and the air-humidii'ying means 12 are steam coils. -They are shown below the tracks 13, but this is immaterial; and the airhumidifying coils are shown as being in part coils located inY water in a water tank 1l, to produce evaporation of water from such tank, and in part as steam-spray coils, though. either type et air-humidi'ying coils maybe used alone, or other types olf airhumidilying means may be used instead. 'llhe steam for both heating andl humidication is shown as being supplied from a main steam supply line 15, which is branched to provide a supply line 16 leading to the heating coils 11 and a supply line 17 leading to the air-humiditying coils 12.

ln the supply line 16 to the heating coils,

11 is a control valve 20, which in the preerred form of my invention is operated by a `fluid-'pressure motor member 21 connected by a pipe 22 to a suitable vapor-pressure thermostat 23 within the kiln 10. 'lhe valve 20 is automaticallyy operated to maintain substantially normal the temperature within the kiln 10; for it the temperature rises in the kiln the vapor-pressure developed in the thermostat 23 also rises to cause the motor member 21 to move the .valve 20 toward closed position, to cut down the supply of" heating steam to the heating coils 11; while it the temperature falls the reverse series of actions takes place,l to increase the supply of steam to the heating coils 11. The motor member 21 and valve 2() are conveniently provided with suitable adjusting means, such as an adjustable weight 2li, by which the temperature which is maintained in the kiln may he varied trom time to time, as the drying proceeds.

ln the supply line 17 to the air-humiditying means 12 is a` controlvalve 30. il have shown this valveas a balanced valve, hav# ing a twin valve-member 31 movable with relation to twin valve-seats 32 to open and close the valve. The valvemember 31 has a valve stem 33, which is connected through a lost-motion connection 3l to a shifter rod atraves 35. The shifter rod 35 is controlled in .response to variations in relative humidity within the kiln 10 to open the valve 30 when the relative humidity drops to a certain low value, say 30%, and to close such valve 30 l when the relative humidity rises to a cer-` tain high value, say 98%, but to be without effect on the valve for intermediate relative humidities. ln consequence, when the valve 30 is closed, the relative humidity ldrops gradually until its low value is reached; whereupon the valve 30 is `opened to admit air-humidiliying steam, to cause the relative humidity to rise until the high value is reached; whereupon the valve 30 is again l closed, and the cycle is repeated. rl`he drop in relative humidity is relatively slow, and the rise relatively rapid.

@ne simple form of mechanism for doing this is shown in Figs. 1 and 2. This ar rangement makes use of the invention set forth in by' prior Patent No. 1,315,517, granted September 9, 1919. ln this arrangement the shifter rod 35 is provided with a thrust plate 36, which is acted on in opposite directions by two lluidpressurc expansible motoremembers 37 and 33, which are connected by two pipes 39 and /lO to two vapor-pressure thermostats i1 ,and 42 respectively. The thermostat l1 is a dry-bulb thermostat, and the pressure therefrom acts in the motor-member 37 to .tend to open the valve 30. The thermostat 42 is a wet-bulb thermostat, and the pressure therefrom acts in the motor-member y' 38 to tend to close the valve 30. rlhe wet- M tu ico

bulb thermostat i2 may be kept wetted in any suitable way, as by a wick 4:3 which overlies such wet-bulb thermostat and dips into water maintained at a constant level in a water tank la by a suitable float valve d5. 'lhe shifter rod 35 is connected to a lever 46, suitably mounted on a fixed pivot t7. The lever i6 carries a normally lined but adjustable weight t3, for adjusting in i the valve operates; andin the arrangement shown in Figs. 2 and 3 are manually adinstable, and` providedwith set-screws;.53 f

by which they are clamped in adjusted position. I

ln the operation of the device shown in Figs. 1 and 2, assume that the valve 30 is closed, so that no. air-humiditying steam is heing supplied to the coils l2, and also assume that the lever t6 is in the toll-line i" position shown in Fig. 2. As no air-humidifying steam is being supplie-d, the relative humidity within the kiln 10 drops, so that there is more evaporation from the wick 43 and therefore a decrease inthe wetbulb temperature with relation to the drybulb temperature. This results' in a decrease inthe pressure exerted in the wet' bulb motor-member 38, so thatl relativelyshifter rod 35 continues, the lever 46 passes4 through tlie horizontal position, so that it tilts downward toward the, left. ,/Then the shifting weight 49 slides down hill along the lever 46 -toward the fulcru-m 47 4until stopped by the. stop 50. This movement of the weight 49 lessens its mechanical advantage, for it helps'hold thel shifter rod 35 downward against the pressure of the' dry-v bulb motor-member 37, and because of this sudden reduction in the resistance, to the operation of the motor member y 37 such dry-bulb motor-member now quickly lifts up the shifter od 35 the remainderv of'its distance. This moves the lever 46 to the dotted-line position in Fig. 2, and also, as

the lost-motion 'of the connection 34 has no'w been taken up, it lifts the valve stemv 33 to open the valve 30. The opening of this valve admits air-humidifying Asteam to the coils 12, and this steam causes the rather rapid humidification of the air4 in the kiln 10, raising it quickly from the low point to which it has fallen to or' nearly to 100%.

This rapid raising of the relative-humid l ity also simultaneously raises to some extent the temperature in the kiln, even though the temperature-control regularly shuts off the heating steam, because the humidifyin steam inevitably brings in heat with it, an

this heat is given up b the Steam, mainly from its latent heat; an this causes a rising in temperature in the lumber, even in the interior thereof. 'In addition, this steam-temporarily softens the surface of the lumber, by`

adding moisture to such surface, .and thus makes easier the passage of moisture there-4 through from the interior. During part of the period during which the relative humidity is dropping, the temperature within the body of the lumberis higher than that within the remainder of the kiln', due to the-heating eii'ect of theplatent heat ofthe steam during the'humidifying period. This is due to the facttliat the interior lof the lumber is heated during the rise. in temperature while humidifying steam is being admitted, but the 'temperature is quickly brought back 'to normal in the air of the kiln-by the temperature controller as soon as'the humidifying steam-is shut oil", thus lowerin the temperature of the air in the kiln elow the temperature which the interior of the lumber has attained. As a result of this overtemperature ,of the interior of the lumber at certain times, a still greater tendency to drive the moisture out to the surface of the lumber `is produced,- as moisture tends to flow in wood from a point of higher temperature to a point of lower temperature. This flow of moisture from the inside out is made easier by the recurrent softening produced by the humidifying steam on the surface parts of the lumber'. The temporary rises of .temperature in the kiln during thelhumidifying periods are superposed on the normally con- Istant temperature which the temperaturecontroller otherwise substantially maintains, and save at these periods do 'not"'interfere with the maintenance of such normally constant temperature. As the relative humidity rises, the evaporation from the wick 43 becomes less rapid, so that the wet-bulb temperature rises; in `consequence of which the pressure developed in the wet-bulb thermol stat 42 increases, and acts through the motor-.member 38 to force the shifting rod 35 gradually downward. At first,'this does not affect the valve vstem 33, because ofthe lost'- motion connection 34; but when the` downward movement of the'shifter rodY 35-'has continued sufliciently far to make the lever f 46 slant downward toward the ri ht, the weight 49 slides outwardon such ever 46 from the fulcrum, 47, until stopped'by the stop 51. This outwardmovem'e'nt of the'v 4weight 49 increases its mechanical `advantage, and causes the shifter rod 35 to move quickly downward the remainder of its distance, to take -up the `remainder of the lost-` motion of the connection 34 andto move the valve member 31 to closed position to shut ofl vthe supplyv ofl air-humidifying' steam. Thereupon the relative humidity in the kiln l0 gradually drops, until the low point is reached. Then the cycle above. described is again repeated. v v

In Fig. 7 .I have given a chart' showing the variation in humidity through several cycles, it being assumed that the dry-bulb temperature in the kiln 10 remains constant, under `the `control of 'the valve 20.-, Indeed, this chart of Fig. 7 indicates lfairly well the conditions even though the. temperature in the kiln 10 is not maintained constant, but is allowed to vary' at random or under `some system of variation'such as a gradual increase throughout the drying period. In other words, eventhough the dry-bulb temperature varies, the apparatus ofvFigsl 1 and 2'will cause a iiuctuation in the relative humiditybetween. relatively constant maximum'. andmmimum values,

though these may not be absolutely constant when the vdry-bulb temperature changes.`

ln the arrangement shown'in Fig. 3, l eliminate the dry-bulb-temperature-controlled motor-member37,land control the valve 30 wholly .by the`- wet-bulb-temperature-controlled -motor-member This is entirely practicable i'ffthere is a definite control of the dry-bulb temperature of the kiln, as by the valve'20 under the control offthe dry-bulb thermostat 23. Fon a. given drybulb temperature, variations f in lrelative humidity cause al corresponding variation in the pressure developed by the motor-meml ber 38, to operate the valve 30 substantially as already explained. For a given temperature in the dry-kiln 10, the chart showing the relative-humidity variations will be substantially that of Fig. 7, just as with the arrangement of Figs. l and 2. It the drybulb temperature is ,changed from time to time, however7 as is usually the lcase in lumber drying by reason ofperiodic increases in temperature from the beginning to the end of the ,drying period, the control arrangement shown in Fig. 3 will produce a chart substantially such as shown in Fig. 8, where the temperature is shown as starting at 130o and as increasing at various times, at the points indicated by the vertical dotted lines. In other` words, with the arrangement shown in Fig. 3, there is a chart such as shown in Fig. 7 for each constant-temperature part of the drying period, but as between successive periods of higher temperature the line indicating the variations in relative humidity is vertically displaced, to a lower position on the chart for each increase in the drybulbtemperature. There are sometimes some advantages in this. v

lt is sometimes desirable to have the successive peaks or troughs, or both, of the humidity-variation line at dit'erent heights. This can be obtained in either of the devices shown, by varying the lengths of successive movements of the weight 49 along-the lever 46. l have shown one arrangement for doing this in Figs. 4, 5, and 6, which otherwise has the same arrangement of parts as in Fig. 2, with the shifterrod 35 operated by the opposing action of the two motor-members 37 and 38 responding respectivelyto the dry-bulb temperature'and to the wetbulb temperature in the dry kiln 10. Here the stops 50 and 51 for the shitting weight 49 are not set by set-screws, as in Figs. 2 and 3, but insteadl one or both of them may be 'automatically shiftable along the lever 46, both stops being shown as thus shiftable. This shifting `of one or both stops may be obtained in any' suitable way, preferably by the ltilting of the lever 46 itself. As shown, each ot the stops 50 and 51 is connected -by a longitudinally extending screw 60, swivlelect inthe stop9 to en externally toothed nut 1.5i are? 61 working between abutments 62 mounted on the lever 46 near its outer end. The teeth oit the two toothed nuts 61 cooperate with tilting dogs 63 carried on any suitable fixed support 64, to cause turning of suchnuts 61 in one direction only, by a ratchet action, upon each tilting movement of the lever 46. |llhis may be arranged to produce any desired movements ot the stops 50 andv 51, or either ot them; and by properly setting the dogs 63 the relative movements of the ltwo stops may be anything` desired. lfn Fig. 9 ll have shown the eil'ect of an automatic movement ot the stop 51 outward by successive tiltings of the lever 46, the stop 50 being assumed to be stationary. By such movementsl of the stops 51 outward, the weight 49 moves successively further outward along the lever 46 upon successive downward swings of the right-hand end of the lever; in consequence of which it is' necessary for the relative humidity to fall to successively lower values in the successive troughs of the humidity curve before the force of the wet-bulb-tempeinture-controlled motor-member 38 is diminished suiliciently to permit the right-hand end of the lever 46 to be tilted upward again.

ln addition to controlling the temperature and the relative humidity in the kiln 10, ,ll may also control the ventilation of the kiln, by theoperation of the same valve 30 which controls the supply of air-humiditying steam. ll'have shown this diagrammatically in Fig. 1. Here a branch pipe from the supply line 17 to the air-humiditying means extends to a fluid-pressure motor 71, shown as of the bellows type, which is connected to operate a lever 72. The lever 72 is suitably connected by a link 73 to a -tlapper valve 74 controlling the entra-nc to the air-intake duct 7 5, and is also connected by a' link 76, a bell-crank 77, and a link 78 to a butteriy valve 79 in the outletliues 80. When the valve 30 is closed, the bellows 71 collapses under the action ofthe weight 150, adjustably carried by the lever 72 and opposing such bellows, to open the valves 74 and 79 during the time the air-humidifying steam'is cut o, so that there will be ventilation and air-circulation during the humidity-decrease parts of the time-humidity curves in Figs. 7, 8, and-9; but when the lowhumidity point has been reached' and the valve 30 has been opened to admit air-hu.- midifying steamy through the supply line 17 to the humidifying coils 12,' part of the steam thus admitted passes through the pipe 70 and expands the bellows 71, to cause the closing of the valves 74 and 79 so long as such air-humidifying steam isl being suplied. When the peaks of the curves in Figs.

8, and 9 are reached to cause the closing of the valve 30, this not only shuts o' the air-humidtying steam, but also permits the amava? steam in the bellows 71 to escape through the'steam-spray holes of the coils 12 so that such bellows again collapses, to cause the opening of the valves 74 to179.

I claim as my invention:

1.-In' combination, a dry-kiln, air-humidifying means therefor, control means for controlling said air-humidifying means, and automatic means for operating said control means to produce alternate lowerings and raisings of the relative humidity of thefair in the dry-kiln, said control means being arranged to shift at each operation the relative-humidity value of its point of operation. n-

2. In combination, a dry-kiln, air-humidifying vmeans therefor, control means for controlling said air-humidifying means, automatic means for operating said control means toA produce alternate lowerings and raisings of the relative humidity of the air in the dry-kiln, said control means being arranged to vshift at each operation the relative-humidity value of its point'of operation, and means for normally maintaining the temperature of said kiln substantiall constant.

3. In combination, a dry-kiln, air-humidil fying means therefor, a control valvefor said air-humidifying means,l means controlled by the wet-bulb temperature ofthe air in said dry-kiln for controlling Said vconf trol valve, and means associated with said trolled jointlyubly control valve and its controlling means for raisingand lowering the relative-humidity value at which the control valve is operated upon eachclosing and opening respectively of the control valve.

4. In combination, a dry-kiln, air-humidifying means therefor, a control valve, for

,said air-humidifying means, means controlled by the wet-bulb temperature of the air in said dry kiln for controlling said control `valve, and a snap-action device associated with'said control valve and its controlling means, said snap-action device being arranged at each operation of said control valve to shift the wet-bulb temperature.

of the operating point of said control valve.

1 5. In combination; adry-kiln, air-humidifying means therefor, a control valve for said air-humidifying means, means con- 'the wet-bulb temperature and the drytemperature of the air in said dry-kiln for controlling said control valve, and means associated with said control valve and its controlling means for raisingr and lowering the relative-humidity va ue at which the control valve is operated upon each closin and opening respectively of the control va ve. v l' 6. In combination, a dry-kiln, air-humidifying means therefor, a control'valve for said air-humidifying means, means controlled jointly by the wet bulb temperature and the dry-bulb temperature of the air in said dry kiln for controlling said control valve, anda snap-action device associated with -said'control valve and its controlling -means, said snap-action device being arranged at each operation of said control valve to change the effective relation between the wet-bulb and dry-bulb temperatures necessary to produce movement of the valve. a

7 In combination, a dry-kiln, air-humidifying means therefor, a control valve for said air-humidifying means, meansA controlled by the wet-bulb temperature of the air in said dry-kiln for controlling said con-v trol valve, means associated with said con trol valve and its controlling means for raising and lowering the lrelative-humidity value at which the control valve is operated upon each closing and opening respectively. of the control valve, heating means for said;I

dry-kiln, and means controlled by the drybulb temperature of the air insaid dry-kiln for controlling'said heating means.

8. In combination, a dry-kiln, air-humidifying means therefor, a control valve forv the air in said drykiln for controlling said i.

heating means. c 9. In combination, a dry-kiln, a1r-hum1d1- fying means therefor, control means for controlling said air-humidifying means, auto-4 matic means for operating said control means to 'produce alternate lowerings and raisings of the relative humidity of the. air in the dry-kiln, said control means being arranged to shift at each operation the relative-humidity 'value of its point'of opera-v tion, 'and means controlled jointly with said air-humidifying vmeans for controlling the air-circulation through said kiln.

10. In combination, a dry-kiln, air-humidifying means therefor, control means for controlling' said air-humidifyin means, automatic means for operating said Acontrol means to produce alternate lowerings and raisings of the relative humidity of the air in the dry-kiln, said control means being arranged to shift at each operation the relative-humidity value of its point of operalas tion, means for normally -maintaining vthe temperatureof said kiln substantially "con,-

stant, and means controlled jointly with said air-humidifying means for controlling the air-circulation through said kiln.

53 intensa ll. lln combination, a dry-kiln, air-humidiitying' means therefor, a contro-l valve for said air-humiditying means, means controlled by the wet-bulb temperature of the air in 'said dry-kiln for controlling said control valve, means associated with said control valve and its controlling means for raising and lowering the relative-humidity value at which the control valve is operated upon each closing and opening respectively ot the control valve, and air-circulation controlmeans for said kiln also controlled by said control valve.

l2. ln `combination, a dry-kiln, air-liumidifying means therefor, a control valve for said air-humiditying means, means controlled by the wet-bulb temperature of the air in said dry-kiln for, controlling said con-I trol valve, and yair-circulation control-means for said kiln also controlled by said control valve. p

13. ln combination, a dry-kiln, air-hu,- midiitying ymeans therefor, a control valve for said air-humidifying meansmeans controlled by the wet-bulb temperature ot the air in said dry kiln for controlling said control valve, a, snap-action device associated with said control valve and its controlling means, and air-circulation control-means for said kiln also controlled by said control valve.

14. ln combination, a dry-kiln, air-huinidifying means therefor., a control valve for said air-humidifying means, means controlled jointly by the wet-bulb temperature and the dry-bulb temperature ot the air in said dry-kiln for controlling said control valve, means associated with said vcontrol valve and its controlling means lfor raising and lowering the relative-humidity value at which the control valve is operated upon each closing and opening respectively ot the control valve, and air-circulation control means for said kiln also controlled by said control valve.

l5. ln combination, a dry-kiln, air-humiditying means therefor, a control valve for said air-humiditying means, means controlled jointl by the wet-bulb temperature and the dryulb temperature ofthe air in said dry-kiln for controlling said control valve,and air-circulation control-means for saild kiln also, controlled 'by said control va ve.'

16. ln combination, a dry-kiln, air-humidiitying means therefor, a control valve :tor said air-humidiiying means, means controlled jointl by the wet-bullo temperature and the d ulb temperature of the air in said dry-kiln for controlling said control valve, a snap-,action device associated with said control valve and its controlling means, and air-circulation control-means tor said kiln also controlled by said control valve.

17. ln combinatiom a dry-kiln, air-humidifying means therefor, a control valve for said air-humidifying means, means controlled by the wet-bulb temperature ot the air in said dry-kiln for controlling said control valve, means associated with said control valve and its controlling means t'or raising and lowering the relative-humidity value at which the control valve is operated upon each closing and opening respectively of the control valve, air circulation controlmeans for said kiln also controlled by said control valve, heating means tor'said drykiln, and means controlled by the dry-bulb temperature of the air in said dry kiln for controlling said heating means.

18. In combination, a dry-kiln, air-humiditying means therefor, a control valve for said air-humidifying means, means controlled bythe Wet-bulb temperature of the air in said dry-kiln for controlling said control valve, air-circulation control means for said kiln also controlled by said controlvalve, heating means for said dry-kiln, and means controlled by the dry-bulb temperature of the air in said dry-kiln for controlling said heating means.

19. ln combination, a dry-kiln, air-liumidifying means therefor, a control valve for said-air-humiditying means, means controlled by the wet-bulb 'temperature ot the air in said dry-kiln for controlling said control valve, a snap-action device associated with said control valve and its controlling means, air-circulation control-means for said kiln also controlled by said .control valve, heating means for said dry-kiln, and means controlled by thev dry-bulb temperature ot' tlieair in said dry-kiln tor controllinff said heating means.

20. n combination, a dry-kiln, air-hnmidifying means therefor, a control valve for said air-humidifying means, means controlled by the wet-bulb temperature ot' the air in said dry-kiln for controlling said control valve, means associated with said control valve and its controlling means for raising and lowering the relative-humidity value at which the 'control valve is operated upon each closing and opening respectively ot the control valve, and means tor periodically varying one or both ot the points to which said relative humidity is raised and lowered.

21. ln combination,a dry-kiln, air humiditying means therefor, a control valve l'or said air-humidifyin'g means, means controlled by the 4wet-bulb temperature of the air in said dry-kiln for controlling said control valve, a snap-action device associated with said control valve and its controlling means, and means for periodically varying one or both of the two different rclative-hnmnlity values at which said snap-action device permits the operation of said control valve.

22. ln combination, a dry-kiln, air-hulllll midifying means therefor, a control valve for said air-humidifying means, means controlled jointly by the wet-bulb temperature and the dry-bulb temperature of the air in said `dry-kiln for controlling said control valve, means associated with said control valve and its vcontrolling means for raising and lowering the relative-humidity value at which the control' valve is operated upon each closing and opening respectively of the control valve, and means for periodically varying one or both of. the points to which said relative humidity is raised and lowered.

23. In combination, a dry-kiln, air-hulmidifying means therefor, a control valve for said air-humidifying means, means controlled jointly by the` wet-bulb temperature and the dry-bulb temperature of the air in said dry-kiln for controlling' said control valve, a snap-action device associated with said control valve and its controlling means, and means for periodically varying one or both of the two different relative-humidity values at which said snap-action device permits the ,operation of said control valve.

' 24. In combination, a dry-kiln, air-humidifying means therefor, control means for controlling said air-humidi-fying means, and automatic means for operating said control means to produce ,alternate lowerings and raisings of the relative-humidity of the air in the dry-kiln, said control means being arranged to shift at each operation the relative-humidity value of its point of operation oppositely to the change such operation produces in said relative humidity.

25. In combination, a control' valve, a power-operated device for operating said control valve, a weight acting to vary the effect of'- said power-operated device, said weight being arranged to act with different force. on said power-operated device during its valve-opening and its valve-closing movenents, and means for controlling said poweroperated device by the relative humidity of a body of air. v

26. In combination, a control valve, two power-operated devices acting in opposition Ion said control valve forl opening and closing it, and means acting to assist one and-v oppose the other of said devices, sald lastnamed means being arranged to act with different force on said power-operated devices during their valve-opening and valveclosing movements.

27. In combination, a control valve, a

y power-operated device for operating said control valve, means acting to vary the effect of said .power-operated device, said means being arranged to act with different force on said power-operated device during its valveopening and 'its valve-closing movements, and means-for controlling said power-operated device bythe relative humidity of v'a vtilting of the lever is reverse body of air.

28. In' combination, a control valve, a power-operated device for positively operating said co-ntrolvalve in both directions, a weight acting to vary the effect oi said power-operated device, said weight being arranged. to act with different force on said power-operated device during its valveopening and its valve-closing'movements,

and a lost-motion connection between said power-operated means and said control valve.

29. In combination, a control valve, two

power-operated-devices acting in opposition on said control valve for opening and closing it, means acting to assist one and oppose the other of said devices, said last-named means being arranged to act with diiferent force on said power-operated devices during their valve-opening and valve'-closing-move- .ments, and a lost-motion connection between 4alost-motion, connection between said power-operated device and said contro member. 31. In combination, a control member, operating means for positively operating said .when the tilting of the lever is reversed, and

control member in both directions, a lever.

connected to said voperatingmeans and-arranged to be tilted in opposite directions from the horizontal by the operation of said operating means, a weight carried by said lever andy shiftable along it to varyits mechanical advantage when the tilting of the lever is reversed, and a lost-motion connection between said operating means and said control member.

32. In combination, a control member, operating means for operating said control member, a lever connected to said operating means and arranged to be tilted in opposite directions from the horizontal by the operation of said operatin means, a weight carried by said lever an shiftable along it to vary its mechanical advantage when the a stop for limiting the shifting of said weight-along :the lever, and meanslfor automatically shiftmeans and arranged to be tilted 1n oppomember, a lever connected'to said operating means and arranged to be tilted in opposite directions from the horizontal by the op-` eration of said operating means, a Weight carried by said lever and shiftable along it to vary its mechanical advantage whenthe'tilting of the lever is reversed, a stop vfor limiting the shifting of said ,weight along the lever, and means for shifting' said stop along said lever by the lever movement periodically in a predetermined direction along said lever.

i 35. In combination, a dry-kiln, air-humidifying means therefor, control means for controlling said air-humidifying means,

'and means responsive' to predetermined moisture-value conditions of the air in the dry-kiln for operating said control means,

said control means being arrangedto vary at each operation the moisture-value of its point of operation.

36. ln combination, -a dry-kiln, air-humidifying means therefor, a control valve for said air-humidifying means, and means responsive to predetermined moisture-value conditions of the air in the dry-kiln for controlling said control valve, said control valve being arranged to vary at each operation the moisture-value of vits point of operation so that it will open and close at p widely different moisture-value conditions.

37. A humidity control apparatus, com-h prising a valve, a iiuid-pressure-operated motor-member which by its movements controls said valve, a wet-bulbthermostat con nected to said motor-member to govern fluid-pressure acting thereon, and a forceexerting deviceco-acting with said motor member and arranged to vary materially the :force with which it acts when the motor-member passes predetermined points in its movements in opposite directions.

38. A humidity control apparatus, comprising a valve, a power-operated motormember which by its lmovements controls said valve, a wet-bulb thermostatconnected to said motor-member lto govern power acting thereon, and a force-exerting device coacting with said motor. member and arranged .t'o vary materially thev force with which it acts when the motor-member passes predetermined points in its movements in opposite directions.

39. A humidity control apparatus, comprising a control member, a power-operated device for voperating said control member, a wet-bulb thermostat for governing power supplied i to` said power-operated device,

and a forceexerting deviceco-acting with said motor-member and arranged to act with different force during the early parts of the movements of said motor-member in opposite directions.

40. A humidity control apparatus, comprising a control valve, a power-operated motor-member which by its movements `controls4 said valve, a. wet-bulb thermostat arranged to' `govern power acting on said motor-member, and means co-operating with said motor-member for producing another force tending to actuate said control ivalve and for varying said additional force -upon each operation of the control valve.

41. A humidity control apparatus, comprising a control valve, and a governing device therefor responsive to variations in moisture-value conditions, said governing vdevice and said valve being arranged at each operation of said control valve to vary the moisture-value of the point of operation of said control valve.

ln witness whereof l have hereunto set my hand at indianapolis', lndiana, this 4th day 'of April, A. D. one thousand nine hundred and twenty-two.

Anfrrinn n. Knien.

ulti 

